After many requests we have created a compact, special balun for single band loop (Sky loop or Delta loop) antennas with specific dimension that present a feedpoint of 70-75 ohms. The CB-1.5-1-1500/5000 is a CUBE(TM) enclosure containing a multi-core, broadband 1.5:1 impedance transformer (50 ohm coax input to 75 ohm balanced output) in series with a 1:1 current balun for extra common mode current choking to keep RF current off the outside of the coax braid and on the antenna where it belongs. The extra choking action also means that the coax feed line will not act as a radiator causing unnecessary RF interference (RFI). Rated for full 1500 watts PEP and 1500 watts CW (ICAS), 1KW Digital. 1.8Mhz – 61 MHz. CB-1.5-1-1500EB is housed in a 4” x 4” x 2” waterproof housing with SO-239 input and stainless steel eye bolts on the side for ease of connection to your wire antenna (or top studs as desired). Top eye bolt acts as an antenna hoist. Also available with top studs for post or wall mounting (Model # CB-1.5-1-1500/5000TS). 5KW models are in a 4 " x 4" x 4" housing. Loop antennas should be cut for 1005/F(MHz) in total length, where F (MHz) is the lowest frequency to be used. For 3.5MHz this equates to 288 foot perimeter (square, delta, multi-side ok). Vertiucal loops with pointy side up and longer bases and fed 1/4 wavelength down one side have a feedpoint impedance near 75 ohms for which this balun is well suited. A very good DX antenna! For unbalanced 50 ohm input to unbalanced 75 ohm output use the CU-1.5-1500 or CU-1.5-5000. Display Note: Product picture is 2:1 balun, 1:1 Unun but actual delivered product is CB/CU-1.5-1-1500/5000 as selected.
Iron powder cores are more stable than ferrites and do not saturate as easily so they are best for tuned circuits, filters, and high power inductors. They come in different “Mixes” for use at different frequencies. For best “Q” use the Mix specified for your frequency.To find the number of turns to give the desired inductance for your coil use the formula below:
Turns = 100 x 
Toroid Dimensions
To order specify core size and mix (e.g. T200A-2). Available in sizes that have µH per 100 turns shown in table.
All iron powder cores are special orders. Please allow one week for shipment after order received.
The iron powder cores shown in the above tables are primarily used for either high power feed line chokes for common mode current reduction or for 4:1 and 9;1 very high power transmission line transformers.
For high power feed line chokes, choose the inside diameter of the iron powder core closest to the transmission line outside diameter and use 6-20 cores at the junction with the antenna feed.
For 4:1 (50/200 or 75/300 ohm) transmission line transformers in the range of 1.8-30 Mhz, select the size appropriate for the power level as follows:
T200A x 2 = 1.5KW
T300A x 2 = 2.5KW
T400A x 2 = 5KW
Use Mix 2 for all the above transmission line transformers. Fully assembled and enclosed units are available for each of the power levels. Click HERE for information.
4:1 transmission line transformers using iron powder cores are typically used for ladder line to 50 ohm coax connections
For .1 – 2 Mhz wide band transformers use Mix 26 which has a higher permeability and requires less turns to achieve a given inductance. Mix 2 has almost constant permeability from 1-30 Mhz. Mix 26 has an initial permeability of 75 at .1 Mhz and gradually decreases to about 10 at 30 Mhz. For high power AM broadcast range (.5-1.7 Mhz) transformer, use Mix 26 to reduce the turn count.
Minimum order for iron powder cores is $50
Shipping on larger cores in quantity may be more than $10 – email/call for quote.